Lubricant composition

ABSTRACT

The present invention provides a lubricating oil composition containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashless friction modifier (D) containing a boronated alkenyl succinimide (D1), which is to be used for a machine equipped with at least one of a wet type brake and a wet type clutch. The lubricating oil composition is not only excellent in oxidation stability but also favorable in an effect for suppressing the generation of squeal and braking properties, and is suitably applicable to machines equipped with a wet type brake or wet type clutch.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition.

BACKGROUND ART

Hydraulic equipment to be mounted on a construction machinery, such as ahydraulic excavator, a crane, a wheel loader, and a bulldozer, isrequired to be operated at a high pressure, a high temperature, or ahigh speed, or under a high load. For that reason, a hydraulic fluidwhich is used in the hydraulic equipment for construction machinery isdemanded to have wear resistance or oxidation stability such that evenwhen used at a high pressure, a high temperature, or a high speed, orunder a high load over a long period of time, it does not impairperformances of the hydraulic equipment.

In addition, for lubrication of a wet type brake or a wet type clutch ofa traction motor, a swing motor, etc., or a wet type disc brake-equippedwinch, etc., equipped in these construction machineries, it is generalthat a hydraulic fluid which is used for the hydraulic equipment is alsoused.

For that reason, the hydraulic fluid which is used for constructionmachinery equipped with a wet type brake or a wet type clutch isrequired to have not only the aforementioned performances as thehydraulic fluid but also a lubricating performance for a wet type brakeor a wet type clutch.

For that reason, in the hydraulic fluid which is used for constructionmachinery equipped with a wet type brake or a wet type clutch, a brakecontrol or the like at the time of swinging is typically performed byincreasing a friction coefficient required to be decreased to a certainextent from the standpoint of application to the hydraulic equipment.

For example, PTL 1 investigates a hydraulic fluid composition forconstruction machinery having excellent wear resistance and sludgegeneration suppression properties even under a high-temperature andhigh-pressure condition while it is a zinc-based one, having a lowkinematic friction coefficient for controlling the actions at the timeof starting or just before stop, and having a high static frictioncoefficient to such an extent that a brake performance by a wet typebrake is not impaired.

In addition to that, PTL 1 discloses a hydraulic fluid composition forconstruction machinery containing a base oil, a zincdialkyldithiophosphate, basic calcium salicylate, and an ashlessfriction modifier containing a nitrogen atom or an oxygen atom but notcontaining phosphorus atom in specified ranges.

CITATION LIST Patent Literature

PTL 1: JP 2014-218625 A

SUMMARY OF INVENTION Technical Problem

Now, for the purpose of suppressing the sludge generation under ahigh-temperature and high-pressure condition, the hydraulic fluidcomposition for construction machinery as described in PTL 1 containscalcium salicylate as a dispersant. In the hydraulic fluid compositionsspecifically disclosed as the working examples, though an effect forsuppressing the sludge generation due to the matter that it containscalcium salicylate is perceived, a ratio of a kinematic frictioncoefficient μ₀ just before stop to a kinematic friction coefficientμ_(d) during operation [μ₀/μ_(d)] is considerably low as 0.750 or less.For that reason, the hydraulic fluid composition for constructionmachinery as described in PTL 1 involves such a concern that a problemof generation of squeal in the wet type clutch test or worsening ofbraking properties is caused, and it is not suited for an application tomachines for which braking properties are particularly required as in acrane.

In view of the aforementioned problems, the present invention has beenmade, and an object thereof is to provide a lubricating oil compositionwhich is not only excellent in oxidation stability but also favorable inan effect for suppressing the generation of squeal and brakingproperties, and which is suitably applicable to machines equipped with awet type brake or a wet type clutch.

Solution to Problem

The present inventors have found that a lubricating oil compositioncontaining zinc dithiophosphate and further containing a metal sulfonateand an ashless friction modifier containing a boronated alkenylsuccinimide is able to solve the aforementioned problem, thereby leadingto accomplishment of the present invention.

Specifically, the present invention relates to the following [1] to [3].

[1] A lubricating oil composition, which is to be used for a machineequipped with at least one of a wet type brake and a wet type clutch,containing a base oil (A), zinc dithiophosphate (B), a metal sulfonate(C), and an ashless friction modifier (D) containing a boronated alkenylsuccinimide (D1).[2] A machine equipped with at least one of a wet type brake and a wettype clutch, including the lubricating oil composition as set forth inthe above [1].[3] A method of using a lubricating oil composition, including using thelubricating oil composition as set forth in the above [1] for a machineequipped with at least one of a wet type brake and a wet type clutch.

Advantageous Effects of Invention

The lubricating oil composition of the present invention is not onlyexcellent in oxidation stability but also favorable in an effect forsuppressing the generation of squeal and braking properties. For thatreason, it is suitably applicable to machines equipped with a wet typebrake or wet type clutch.

DESCRIPTION OF EMBODIMENTS

In this specification, the content of each of atoms means a value asmeasured in conformity with the following standards.

-   -   Zinc atom (Zn), calcium atom (Ca), boron atom (B), and        phosphorus atom (P): Measured in conformity with JPI-5S-38-03.    -   Sulfur atom (S): Measured in conformity with JIS K2541-6.    -   Nitrogen atom (N): Measured in conformity with JIS K2609.

[Lubricating Oil Composition]

The lubricating oil composition of the present invention contains a baseoil (A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashlessfriction modifier (D) containing a boronated alkenyl succinimide (D1).

The lubricating oil composition of an embodiment of the presentinvention may further contain an antioxidant (E) according to thecontent of the zinc dithiophosphate (B).

The lubricating oil composition of an embodiment of the presentinvention may also contain other additives for lubricating oil notcorresponding to the aforementioned components within a range where theeffects of the present invention are not impaired.

In the lubricating oil composition of an embodiment of the presentinvention, the total content of the component (A), the component (B),the component (C), and the component (D) based on the total amount (100%by mass) of the lubricating oil composition is preferably 60% by mass ormore, more preferably 70% by mass or more, still more preferably 75% bymass or more, and yet still more preferably 80% by mass or more, and itis typically 100% by mass or less, preferably 99.0% by mass or less, andmore preferably 98.0% by mass or less.

In the lubricating oil composition of an embodiment of the presentinvention, the total content of the component (A), the component (B),the component (C), the component (D), and the component (E) based on thetotal amount (100% by mass) of the lubricating oil composition ispreferably 65% by mass or more, more preferably 70% by mass or more,still more preferably 75% by mass or more, and yet still more preferably80% by mass or more, and it is typically 100% by mass or less,preferably 99.5% by mass or less, and more preferably 99.0% by mass orless.

The lubricating oil composition of the present invention is one to beused for a machine equipped with at least one of a wet type brake and awet type clutch.

As mentioned above, in a machine equipped with a wet type brake or a wettype clutch, it is general that a lubricating oil composition which isused for the hydraulic equipment is also used for a wet type brake or awet type clutch of a traction motor or a swing motor, etc. with whichthe foregoing machine is equipped.

For that reason, the lubricating oil composition which is used for amachine equipped with a wet type brake or a wet type clutch is requiredto have not only excellent oxidation stability that is a performance asthe hydraulic fluid but also such characteristics that a frictioncoefficient is high to a certain extent, and an effect for suppressingthe generation of squeal or braking properties are favorable so as tomake it applicable for lubrication of a wet type brake or a wet typeclutch.

Now, in the lubricating oil composition as disclosed in PTL 1, etc.,which is obtained by blending a metal salicylate as a dispersanttogether with a base oil and zinc dithiophosphate, a ratio of akinematic friction coefficient μ₀ just before stop to a kinematicfriction coefficient μ_(d) during operation [μ₀/μ_(d)] tends to becomelow. For example, in the lubricating oil compositions shown in theworking examples of the PTL 1, the foregoing ratio [μ₀/μ_(d)] isconsiderably low as 0.750 or less.

As mentioned above, in such a lubricating oil composition, on theoccasion when applied to a wet type brake or a wet type clutch, thegeneration of squeal or worsening of braking properties to be caused dueto a decrease of the friction coefficient is feared. In particular, whenapplied to a machine for which braking properties are required, such asa crane and a winch, it is expected to be difficult for control ofdelicate movements of the winch.

On the other hand, in the lubricating oil composition of the presentinvention, in view of the fact that it contains, as a dispersant, themetal sulfonate (C) but not a metal salicylate, together with the baseoil (A) and the zinc dithiophosphate (B) and further contains, as afriction modifier, the ashless friction modifier (D) containing theboronated alkenyl succinimide (D1) containing a nitrogen atom and anoxygen atom, not only excellent oxidation stability is kept, but also aneffect for suppressing the generation of squeal is high, and brakingproperties are improved, too.

Each of the components which are contained in the lubricating oilcomposition of an embodiment of the present invention is hereunderdescribed.

<Base Oil (A)>

The base oil (A) which is contained in the lubricating oil compositionof the present invention may be a mineral oil, may be a synthetic oil,or may be a mixed oil of a mineral oil and a synthetic oil.

Examples of the mineral oil include atmospheric residues obtainedthrough atmospheric distillation of crude oils, such as paraffin-basedcrude oils, intermediate-base crude oils, and naphthene-based crudeoils; distillates obtained through reduced-pressure distillation of suchatmospheric residues; mineral oils obtained by purifying the distillatesthrough one or more purification treatments, such as solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, and hydrorefining; and mineral oils (GTL) obtainedby isomerizing a wax (GTL wax (Gas To Liquids WAX)) which is obtained bysynthesis of a natural gas through the Fischer-Tropsch method, etc.

These mineral oils may be used alone or may be used in combination oftwo or more thereof.

Of these, as the mineral oil which is used in an embodiment of thepresent invention, it is preferred to contain a mineral oil having beensubjected to one or more purification treatments, such as solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, and hydrorefining, or a mineral oil obtained byisomerizing a GTL wax.

As the mineral oil, it is preferred to contain a mineral oil grouped inGroup 2 or Group 3 in the base oil category by API (American PetroleumInstitute) or a mineral oil obtained by isomerizing a GTL wax; and it ismore preferred to contain a mineral oil grouped in the foregoing Group 3or a mineral oil obtained by isomerizing a GTL wax.

Examples of the synthetic oil include synthetic oils, such aspoly-α-olefins, e.g., an α-olefin homopolymer and an α-olefin copolymer(for example, an α-olefin copolymer having 8 to 14 carbon atoms, e.g.,an ethylene-α-olefin copolymer); isoparaffins; esters, e.g., a polyolester and a dibasic acid ester; ethers, e.g., polyphenyl ether;polyalkylene glycols; alkylbenzenes; and alkylnaphthalenes.

These synthetic oils may be used alone or may be used in combination oftwo or more thereof.

Of these, as the synthetic oil which is used in an embodiment of thepresent invention, it is preferred to contain one or more synthetic oilsselected from poly-α-olefins, various esters, and polyalkylene glycols.

A kinematic viscosity at 40° C. of the base oil (A) is preferably 10 to150 mm²/s, more preferably 12 to 120 mm²/s, and still more preferably 15to 100 mm²/s.

A viscosity index of the base oil (A) is preferably 80 or more, morepreferably 100 or more, and still more preferably 110 or more.

In this specification, the “kinematic viscosity at 40° C.” and the“viscosity index” mean values as measured in conformity of JIS K2283.

In the case where the base oil (A) is a mixed oil of two or moreselected from mineral oils and synthetic oils, the kinematic viscosityand the viscosity index of the mixed oil have to only fall within theaforementioned ranges, respectively.

In the lubricating oil composition of an embodiment of the presentinvention, the content of the base oil (A) based on the total amount(100% by mass) of the lubricating oil composition is typically 55% bymass or more, preferably 60% by mass or more, more preferably 65% bymass or more, still more preferably 70% by mass or more, and yet stillmore preferably 75% by mass or more, and it is preferably 98% by mass orless, more preferably 97% by mass or less, still more preferably 95% bymass or less, and yet still more preferably 93% by mass or less.

<Zinc Dithiophosphate (B)>

Since the lubricating oil composition of the present invention containsthe zinc dithiophosphate (B), it improves wear resistance and oxidationstability and effectively suppresses metal wear and oxidationdegradation generated following the use.

The zinc dithiophosphate (B) which is contained in the lubricating oilcomposition of an embodiment of the present invention is preferably acompound represented by the following general formula (b-1).

The zinc dithiophosphate (B) may be used alone or may be used incombination of two or more thereof.

In the formula (b-1), R¹ to R⁴ each independently represent ahydrocarbon group and may be the same as or different from each other.

Specific examples of the hydrocarbon group which may be selected as R¹to R⁴ include alkyl groups, such as a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group, a 2-ethylhexyl group, a nonyl group, a decylgroup, an undecyl group, a dodecyl group, a tridecyl group, a tetradecylgroup, a pentadecyl group, a hexadecyl group, a heptadecyl group, and anoctadecyl group; alkenyl groups, such as an octenyl group, a nonenylgroup, a decenyl group, an undecenyl group, a dodecenyl group, atridecenyl group, a tetradecenyl group, and a pentadecenyl group;cycloalkyl groups, such as a cyclohexyl group, a dimethylcyclohexylgroup, an ethylcyclohexyl group, a methylcyclohexylmethyl group, acyclohexylethyl group, a propylcyclohexyl group, a butylcyclohexylgroup, and a heptylcyclohexyl group; aryl groups, such as a phenylgroup, a naphthyl group, an anthracenyl group, a biphenyl group, and aterphenyl group; alkylaryl groups, such as a tolyl group, adimethylphenyl group, a butylphenyl group, a nonylphenyl group, amethylbenzyl group, and a dimethylnaphthyl group; and arylalkyl groups,such as a phenylmethyl group, a phenylethyl group, and a diphenylmethylgroup.

Of these, an alkyl group is preferred as R¹ to R⁴.

Though the alkyl group may be either a linear alkyl group or a branchedalkyl group, it is preferably a branched alkyl group.

The carbon number of the hydrocarbon group which may be selected as R¹to R⁴ is preferably 1 to 20, more preferably 3 to 16, still morepreferably 4 to 12, and yet still more preferably 5 to 10.

In the lubricating oil composition of an embodiment of the presentinvention, from the viewpoint of not only more improving the oxidationstability and enhancing the effect for suppressing the sludgedeposition, but also providing a lubricating oil composition withexcellent wear resistance, the content of the component (B) as expressedin terms of a zinc atom based on the total amount (100% by mass) of thelubricating oil composition is preferably 100 ppm by mass or more, morepreferably 150 ppm by mass or more, still more preferably 200 ppm bymass or more, and yet still more preferably 250 ppm by mass or more, andfrom the viewpoint of more improving the wear resistance, it is even yetstill more preferably 500 ppm by mass or more, and especially preferably600 ppm by mass or more.

So long as the content of the component (B) as expressed in terms of azinc atom is 500 ppm by mass or more, even when an antioxidant (E) asmentioned later is not separately blended, it becomes possible toprepare a lubricating oil composition having an effect for suppressingthe sludge deposition.

From the viewpoint of providing a lubricating oil composition capable ofregulating the friction coefficient to a predetermined value or more andsuppressing evils, such as generation of squeal and worsening of brakingproperties, the content of the component (B) as expressed in terms of azinc atom based on the total amount (100% by mass) of the lubricatingoil composition is preferably 2,000 ppm by mass or less, more preferably1,500 ppm by mass or less, still more preferably 1,200 ppm by mass orless, and yet still more preferably 1,000 ppm by mass or less.

In the lubricating oil composition of an embodiment of the presentinvention, as for the content (blending amount) of the component (B),though the content as expressed in terms of a zinc atom may be regulatedso as to fall within the aforementioned range, it is typically 0.01 to2.00% by mass, preferably 0.01 to 1.50% by mass, more preferably 0.01 to1.00% by mass, still more preferably 0.05 to 0.90% by mass, yet stillmore preferably 0.10 to 0.85% by mass, and especially preferably 0.20 to0.80% by mass based on the total amount (100% by mass) of thelubricating oil composition.

<Metal Sulfonate (C)>

Since the lubricating oil composition of the present invention containsthe metal sulfonate (C), not only the effect for improving the oxidationstability owing to addition of the component (B) is effectivelyrevealed, but also evils, such as worsening of braking properties, canbe suppressed.

From the aforementioned viewpoint, the metal sulfonate (C) is preferablya metal sulfonate containing a metal atom selected from alkali metalsand an alkaline earth metals; and more preferably a metal sulfonatecontaining a metal atom selected from a sodium atom, a calcium atom, amagnesium atom, and a barium atom. In particular, from the viewpoint ofproviding a lubricating oil composition in which the frictioncoefficient in a high-speed region is appropriately increased, and thebraking properties are more improved, it is still more preferred tocontain calcium sulfonate.

In this specification, the “alkali metal atom” refers to a lithium atom(Li), a sodium atom (Na), a potassium atom (K), a rubidium atom (Rb), acesium atom (Cs), and a francium atom (Fr).

The “alkaline earth metal atom” refers to a beryllium atom (Be), amagnesium atom (Mg), a calcium atom (Ca), a strontium atom (Sr), and abarium atom (Ba).

In the lubricating oil composition of an embodiment of the presentinvention, the content of the calcium sulfonate in the component (C)based on the total amount (100% by mass) of the component (C) which iscontained in the lubricating oil composition is preferably 70 to 100% bymass, more preferably 80 to 100% by mass, still more preferably 90 to100% by mass, and yet still more preferably 95 to 100% by mass.

The metal sulfonate (C) which is contained in the lubricating oilcomposition of an embodiment of the present invention is preferably acompound represented by the following general formula (c-1).

The metal sulfonate (C) may be used alone or may be used in combinationof two or more thereof.

In the general formula (c-1), M is a metal atom; preferably an alkalimetal or an alkaline earth metal; more preferably a sodium atom, acalcium atom, a magnesium atom, or a barium atom; still more preferablya calcium atom or a magnesium atom; and yet still more preferably acalcium atom.

p is a valence of M and is 1 or 2.

Examples of R include a hydrogen atom, an alkyl group having 1 to 18carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkylgroup having 3 to 18 ring carbon atoms, an aryl group having 6 to 18ring carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, andan arylalkyl group having 7 to 18 carbon atoms.

Though the metal sulfonate (C) may be any of a neutral salt, a basicsalt, an overbased salt, and a mixture thereof, it is preferred tocontain an overbased salt.

In the case where the metal sulfonate (C) is a neutral salt, a basenumber of the neutral salt is preferably 0 to 30 mgKOH/g, morepreferably 0 to 25 mgKOH/g, and still more preferably 0 to 20 mgKOH/g.

In the case where the metal sulfonate (C) is a basic salt or anoverbased salt, a base number of the basic salt or overbased salt ispreferably 100 to 600 mgKOH/g, more preferably 120 to 550 mgKOH/g, stillmore preferably 160 to 500 mgKOH/g, and yet still more preferably 200 to480 mgKOH/g.

In this specification, the “base number” means a base number measured bythe perchloric acid method in conformity with Item 7 of JIS K2501“Petroleum Products and Lubricating Oils-Neutralization Number TestingMethod.”

In the lubricating oil composition of an embodiment of the presentinvention, from the viewpoint of providing a lubricating oil compositionin which the friction coefficient in a high-speed region isappropriately increased, and the braking properties are improved, thecontent of the component (C) as expressed in terms of a metal atom basedon the total amount (100% by mass) of the lubricating oil composition ispreferably 200 ppm by mass or more, more preferably 300 ppm by mass ormore, still more preferably 400 ppm by mass or more, yet still morepreferably 500 ppm by mass or more, even yet still more preferably 1,000ppm by mass or more, and even still more preferably 1,200 ppm by mass ormore.

From the viewpoint of providing a lubricating oil composition which maymore effectively suppress the generation of squeal, the content of thecomponent (C) as expressed in terms of a metal atom based on the totalamount (100% by mass) of the lubricating oil composition is preferably4,000 ppm by mass or less, more preferably 3,500 ppm by mass or less,still more preferably 2,500 ppm by mass or less, and yet still morepreferably 2,000 ppm by mass or less.

In the lubricating oil composition of an embodiment of the presentinvention, as for the content (blending amount) of the component (C),though the content as expressed in terms of a metal atom may beregulated so as to fall within the aforementioned range, it ispreferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.7% by mass,still more preferably 0.10 to 2.4% by mass, and yet still preferably0.20 to 2.0% by mass based on the total amount (100% by mass) of thelubricating oil composition.

In the lubricating oil composition of an embodiment of the presentinvention, though a metal salicylate may be contained within a rangewhere the effects of the present invention are not impaired, from theviewpoint of providing a lubricating oil composition in which thefriction coefficient in a high-speed region is appropriately increased,and the braking properties are more improved, it is preferred that thecontent of the metal salicylate is low as far as possible.

Specifically, the content of the metal salicylate based on the totalamount (100% by mass) of the lubricating oil composition is preferablyless than 0.03% by mass, more preferably less than 0.01% by mass, stillmore preferably less than 0.001% by mass, and yet still more preferablyless than 0.0001% by mass.

The content of the metal salicylate relative to the total amount (100%by mass) of the component (C) which is contained in the lubricating oilcomposition is preferably less than 10% by mass, more preferably lessthan 6% by mass, still more preferably less than 3% by mass, and yetstill more preferably less than 1% by mass.

<Ashless Friction Modifier (D)>

Since the lubricating oil composition of the present invention containsthe ashless friction modifier (D) containing the boronated alkenylsuccinimide (D1), not only the effect for improving the oxidationstability owing to addition of the component (B) is effectivelyrevealed, but also evils, such as worsening of braking properties, canbe suppressed.

In particular, in view of the fact that the component (D1) is contained,the effect for suppressing evils, such as generation of squeal andworsening of braking properties, may be conspicuously improved ascompared with the case of using only the component (C).

In the lubricating oil composition of an embodiment of the presentinvention, from the viewpoint of not only more effectively revealing theeffect for improving the oxidation stability owing to addition of thecomponent (B) but also more suppressing evils, such as generation ofsqueal and worsening of braking properties, it is preferred that thecomponent (D) contains the boronated alkenyl succinimide (D1) and analkenyl group-containing unsaturated amine (D2).

A content ratio of the component (D1) to the component (D2) [(D1)/(D2)]is preferably 2 to 100, more preferably 3 to 80, still more preferably 4to 60, yet still more preferably 5 to 50, and even yet still morepreferably 7 to 40 in terms of a mass ratio.

When the aforementioned mass ratio [(D1)/(D2)] is 2 or more, the effectfor suppressing worsening of braking properties is more readilyrevealed. On the other hand, when the mass ratio [(D1)/(D2)] is 100 orless, the effect for suppressing the generation of squeal is morereadily revealed.

The lubricating oil composition of an embodiment of the presentinvention may contain, as the ashless friction modifier (C), otherashless friction modifier than the components (D1) and (D2) within arange where the effects of the present invention are not impaired.

However, in the lubricating oil composition of an embodiment of thepresent invention, the content of the component (D1) based on the totalamount (100% by mass) of the component (D) which is contained in thelubricating oil composition is preferably 50% by mass or more, morepreferably 60% by mass or more, still more preferably 70% by mass ormore, and yet still more preferably 80% by mass or more.

In the lubricating oil composition of an embodiment of the presentinvention, the total content of the components (D1) and (D2) based onthe total amount (100% by mass) of the component (D) which is containedin the lubricating oil composition is preferably 60 to 100% by mass,more preferably 70 to 100% by mass, still more preferably 80 to 100% bymass, and yet still more preferably 90 to 100% by mass.

In the lubricating oil composition of an embodiment of the presentinvention, the content (blending amount) of the component (D) based onthe total amount (100% by mass) of the lubricating oil composition ispreferably 0.05 to 7.0% by mass, more preferably 0.10 to 5.0% by mass,still more preferably 0.20 to 4.0% by mass, and yet still morepreferably 0.30 to 3.2% by mass.

In the lubricating oil composition of an embodiment of the presentinvention, the content of a nitrogen atom derived from the component (D)based on the total amount (100% by mass) of the lubricating oilcomposition is preferably 15 to 900 ppm by mass, more preferably 40 to700 ppm by mass, still more preferably 55 to 500 ppm by mass, and yetstill more preferably 100 to 350 ppm by mass.

[Boronated Alkenyl Succinimide (D1)]

The boronated alkenyl succinimide (D1) which is used in the presentinvention is a boronated product of an alkenyl succinimide, and examplesof the boronated product include boron oxide, a boron halide, boricacid, boric anhydride, a boric acid ester, and an ammonium salt of boricacid.

In an embodiment of the present invention, the boronated alkenylsuccinimide (D1) is preferably a boronated product of a compoundrepresented by the following general formula (d-11) or (d-12).

The component (D1) may also be a boronated product of polybutenylsuccinimide obtained through a reaction between a compound representedby the following general formula (d-11) or (d-12) and at least onecompound selected from an alcohol, an aldehyde, a ketone, analkylphenol, a cyclic carbonate, an epoxy compound, and an organic acid.

In the general formulae (d-11) and (d-12), R^(A), R^(A1), and R^(A2) areeach independently an alkenyl group having a weight average molecularweight (Mw) of 500 to 3,000 (preferably 1,000 to 3,000).

R^(B), R^(B1), and R^(B2) are each independently an alkylene grouphaving 2 to 5 carbon atoms.

x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and morepreferably 3 or 4.

x2 is an integer of 0 to 10, preferably an integer of 1 to 4, and morepreferably 2 or 3.

Examples of the alkenyl group which may be selected as R^(A), R^(A1),and R^(A2) include a polybutenyl group, a polyisobutenyl group, and agroup containing an ethylene-propylene unit. Of these, a polybutenylgroup or a polyisobutenyl group is preferred.

The compound represented by the general formula (d-11) can be, forexample, produced by allowing an alkenyl succinic anhydride obtainedthrough a reaction between a polyolefin and maleic anhydride, to reactwith a polyamine.

Examples of the polyolefin include polymers obtained throughpolymerization of one or more compounds selected from (α-olefins having2 to 8 carbon atoms. Of these, a copolymer of isobutene and 1-butene ispreferred.

Examples of the polyamine include simple diamines, such asethylenediamine, propylenediamine, butylenediamine, andpentylenediamine; polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine,di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine,and pentapentylenehexamine; and piperazine derivatives, such asaminoethylpiperazine.

The compound represented by the general formula (d-12) can be, forexample, produced by allowing an alkenyl succinic anhydride obtainedthrough a reaction between the aforementioned polyolefin and maleicanhydride, to react with the aforementioned polyamine.

In the lubricating oil composition of an embodiment of the presentinvention, from the viewpoint of effectively suppressing evils, such asgeneration of squeal and worsening of braking properties, a mass ratio[B/N] of a boron atom to a nitrogen atom constituting the component (D1)is preferably 0.2 to 3.0, more preferably 0.4 to 2.5, still morepreferably 0.6 to 2.0, and yet still more preferably 0.7 to 1.5.

In the lubricating oil composition of an embodiment of the presentinvention, the content of the component (D1) as expressed in terms of aboron atom based on the total amount (100% by mass) of the lubricatingoil composition is preferably 30 to 600 ppm by mass, more preferably 50to 500 ppm by mass, still more preferably 60 to 400 ppm by mass, and yetstill more preferably 80 to 300 ppm by mass.

In the lubricating oil composition of an embodiment of the presentinvention, the content of the component (D1) as expressed in terms of anitrogen atom based on the total amount (100% by mass) of thelubricating oil composition is preferably 10 to 800 ppm by mass, morepreferably 30 to 600 ppm by mass, still more preferably 50 to 400 ppm bymass, and yet still more preferably 80 to 300 ppm by mass.

In the lubricating oil composition of an embodiment of the presentinvention, as for the content (blending amount) of the component (D1),though the content as expressed in terms of a boron atom may beregulated so as to fall within the aforementioned range, it ispreferably 0.05 to 4.0% by mass, more preferably 0.10 to 3.0% by mass,still more preferably 0.20 to 2.5% by mass, and yet still morepreferably 0.30 to 2.0% by mass based on the total amount (100% by mass)of the lubricating oil composition.

[Alkenyl Group-Containing Unsaturated Amine (D2)]

Examples of the alkenyl group-containing unsaturated amine (D2) which isused in an embodiment of the present invention include primary totertiary unsaturated amines having 1 to 3 alkenyl groups.

The carbon number of the alkenyl group is preferably 2 to 30, morepreferably 4 to 26, still more preferably 8 to 24, and yet still morepreferably 10 to 20.

Though the alkenyl group may be either a linear alkenyl group or abranched alkenyl group, it is preferably a linear alkenyl group.

In an embodiment of the present invention, it is preferred that theunsaturated amine (D2) contains a primary unsaturated amine (D21) havingan alkenyl group having 2 to 30 carbon atoms.

In the lubricating oil composition of an embodiment of the presentinvention, the content of the primary unsaturated amine (D21) in thecomponent (D2) based on the total amount (100% by mass) of the component(D2) which is contained in the lubricating oil composition is preferably70 to 100% by mass, more preferably 80 to 100% by mass, still morepreferably 90 to 100% by mass, and yet still more preferably 95 to 100%by mass.

The primary unsaturated amine (D21) is preferably a compound representedby the following general formula (d-2).

H₂N—(CH₂)_(z1)—CH═CH—(CH₂)_(z2)—H  (d-2)

In the general formula (d-2), z1 and z2 are each independently aninteger of 0 or more, and (z1+z2) is an integer of 0 to 28. (z1+z2) ispreferably 2 to 24, more preferably 6 to 22, and still more preferably 7to 18.

In the lubricating oil composition of an embodiment of the presentinvention, the content of the component (D2) as expressed in terms of anitrogen atom based on the total amount (100% by mass) of thelubricating oil composition is preferably 5 to 100 ppm by mass, morepreferably 10 to 80 ppm by mass, still more preferably 15 to 60 ppm bymass, and yet still more preferably 20 to 50 ppm by mass.

In the lubricating oil composition of an embodiment of the presentinvention, as for the content (blending amount) of the component (D2),though the content as expressed in terms of a nitrogen atom may beregulated so as to fall within the aforementioned range, it ispreferably 0.001 to 3.0% by mass, more preferably 0.005 to 2.0% by mass,still more preferably 0.01 to 1.5% by mass, and yet still morepreferably 0.02 to 1.2% by mass based on the total amount (100% by mass)of the lubricating oil composition.

[Other Ashless Friction Modifier (D) than Components (D1) and (D2)]

The lubricating oil composition of an embodiment of the presentinvention may contain, as the ashless friction modifier (C), otherashless friction modifier than the components (D1) and (D2) within arange where the effects of the present invention are not impaired.

Examples of the other ashless friction modifier include an aliphaticamine having an alkyl group having 2 to 30 carbon atoms, other than thecomponents (D1) and (D2); a compound having an alkenyl group or an alkylgroup each having 2 to 30 carbon atoms, which is selected from a fattyacid ester, a fatty acid amide, a fatty acid, an aliphatic alcohol, andan aliphatic ether; a phosphoric acid ester; and a non-boronated alkenylsuccinimide.

In the lubricating oil composition of an embodiment of the presentinvention, a non-boronated alkenyl succinimide may be contained within arange where the effects of the present invention are not impaired;however, it is preferred that the content of the non-boronated alkenylsuccinimide is low.

Specifically, the content of the non-boronated alkenyl succinimide basedon the total amount (100% by mass) of the component (D1) which iscontained in the lubricating oil composition is preferably less than 10%by mass, more preferably less than 6% by mass, still more preferablyless than 3% by mass, and yet still more preferably less than 1% bymass.

<Antioxidant (E)>

The lubricating oil composition of an embodiment of the presentinvention may further contain an antioxidant (E) according to thecontent of the zinc dithiophosphate (B).

Examples of the antioxidant (E) include a phenol-based antioxidant, anamine-based antioxidant, a molybdenum-based antioxidant, a sulfur-basedantioxidant, and a phosphorus-based antioxidant.

In an embodiment of the present invention, the antioxidant (E) may beused alone or may be used in combination of two or more thereof.

Of these, in an embodiment of the present invention, from the viewpointof more improving the oxidation stability, it is preferred that theantioxidant (E) contains a phenol-based antioxidant (E1) and anamine-based antioxidant (E2).

Examples of the phenol-based antioxidant (E1) include monophenol-basedantioxidants, such as 2,6-di-t-butylphenol,2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol,isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, andoctadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; diphenol-basedantioxidants, such as 4,4′-methylenebis(2,6-di-t-butylphenol) and2,2′-methylenebis(4-ethyl-6-t-butylphenol); and hindered phenol-basedantioxidants.

The amine-based antioxidant (E2) is preferably an aromatic aminecompound, and more preferably at least one selected from a diphenylaminecompound and a naphthylamine-based compound.

Examples of the diphenylamine-based compound includemonoalkyldiphenylamine-based compounds having one alkyl group having 1to 30 carbon atoms (preferably 4 to 30 carbon atoms, and more preferably8 to 30 carbon atoms), such as monooctyldiphenylamine andmonononyldiphenylamine; dialkyldiphenylamine compounds having two alkylgroups having 1 to 30 carbon atoms (preferably 4 to 30 carbon atoms, andmore preferably 8 to 30 carbon atoms), such as4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine,4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine,4,4′-dioctyldiphenylamine, and 4,4′-dinonyldiphenylamine;polyalkyldiphenylamine-based compounds having three or more alkyl groupshaving 1 to 30 carbon atoms (preferably 4 to 30 carbon atoms, and morepreferably 8 to 30 carbon atoms), such as tetrabutyldiphenylamine,tetrahexyldiphenylamine, tetraoctyldiphenylamine, andtetranonyldiphenylamine; and 4,4′-bis(α,α-dimethylbenzyl)diphenylamine.

Examples of the naphthylamine-based compound include 1-naphthylamine,phenyl-1-naphthylamine, butylphenyl-1-naphthylamine,pentylphenyl-1-naphthylamine, hexylphenyl-1-naphthylamine,heptylphenyl-1-naphthylamine, octylphenyl-1-naphthylamine,nonylphenyl-1-naphthylamine, decylphenyl-1-naphthylamine, anddodecylphenyl-1-naphthylamine.

Examples of the molybdenum-based antioxidant include a molybdenum aminecomplex obtained through a reaction between molybdenum trioxide and/ormolybdic acid and an amine compound.

Examples of the sulfur-based antioxidant includedilauryl-3,3′-thiodipropionate.

Examples of the phosphorus-based antioxidant include a phosphite anddiethyl 3,5-di-t-butyl-4-hydroxybenzylphosphonate.

In the lubricating oil composition of an embodiment of the presentinvention, from the viewpoint of more improving the oxidation stability,a mass ratio [(E1)/(E2)] of the component (E1) to the component (E2) ispreferably 1/6 to 6/1, more preferably 1/5 to 5/1, still more preferably1/4 to 4/1, and yet still more preferably 1/3.5 to 3.5/1.

In the lubricating oil composition of an embodiment of the presentinvention, the total content of the components (E1) and (E2) based onthe total amount (100% by mass) of the component (E) which is containedin the lubricating oil composition is preferably 60 to 100% by mass,more preferably 70 to 100% by mass, still more preferably 80 to 100% bymass, and yet still more preferably 90 to 100% by mass.

In the lubricating oil composition of an embodiment of the presentinvention, the content (blending amount) of the component (E) based onthe total amount (100% by mass) of the lubricating oil composition ispreferably 0.01 to 10.0% by mass, more preferably 0.05 to 7.0% by mass,still more preferably 0.10 to 5.0% by mass, and yet still morepreferably 0.20 to 3.0% by mass.

In the lubricating oil composition in which the content of the component(B) as expressed in terms of a zinc atom is 500 ppm by mass or more,even when the antioxidant (E) is not blended, the effect for suppressingthe sludge deposition can be made high.

For that reason, the lubricating oil composition may not contain theantioxidant (E).

<Other Additives for Lubricating Oil>

The lubricating oil composition of an embodiment of the presentinvention may contain other additives for lubricating oil notcorresponding to the aforementioned components (B) to (E) within a rangewhere the effects of the present invention are not impaired.

Examples of the other additives for lubricating oil include a viscosityindex improver, a flow point depressant, an anti-wear agent, an extremepressure agent, a metal-based friction modifier, a rust inhibitor, ametal deactivator, a demulsifier, and an anti-foaming agent.

Each of such additives for lubricating oil may be used alone or may beused in combination of two or more thereof.

Though the content of each of such additives for lubricating oil can beproperly regulated within a range where the effects of the presentinvention are not impaired, it is typically 0.001 to 15% by mass,preferably 0.005 to 10% by mass, and more preferably 0.01 to 8% by massbased on the total amount (100% by mass) of the lubricating oilcomposition.

In this specification, taking into consideration handling properties andsolubility in the base oil (A), the additive, such as a viscosity indeximprover and an anti-foaming agent, may be blended in a form of asolution having been diluted with and dissolved in a part of the basedoil (A), with other components. In such a case, in this specification,the aforementioned content of the additive, such as an anti-foamingagent and a viscosity index improver, means the content as expressed interms of the effective component excluding a diluent oil (expressed interms of the resin content).

Examples of the viscosity index improver include polymers, such as anon-dispersant-type polymethacrylate, a dispersant-typepolymethacrylate, an olefin-based copolymer (for example, anethylene-propylene copolymer), a dispersant-type olefin-based copolymer,and a styrene-based copolymer (for example, a styrene-diene copolymerand a styrene-isoprene copolymer).

Though a weight average molecular weight (Mw) of such a viscosity indeximprover is typically 500 to 1,000,000, preferably 5,000 to 100,000, andmore preferably 10,000 to 50,000, it is properly set according to thekind of the polymer.

In this specification, the weight average molecular weight (Mw) of eachof the components is a value as expressed in terms of standardpolystyrene as measured by means of gel permeation chromatography (GPC).

Examples of the flow point depressant include ethylene-vinyl acetatecopolymers, condensation products of chloroparaffin and naphthalene,condensation products of chloroparaffin and phenol, polymethacrylates,and polyalkylstyrenes.

Examples of the anti-wear agent or the extreme pressure agent includezinc phosphate that is a phosphorus compound other than the component(B); sulfur-containing compounds, such as zinc dithiocarbamate,molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides,sulfurized olefins, sulfurized oils and fats, sulfurized esters,thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containingcompounds, such as phosphorous acid esters, phosphoric acid esters,phosphonic acid esters, and amine salts or metal salts thereof; andsulfur- and phosphorus-containing compounds, such as thiophosphorousacid esters, thiophosphoric acid esters, thiophosphonic acid esters, andamine salts or metal salts thereof.

Examples of the metal-based friction modifier include molybdenum-basedfriction modifiers, such as molybdenum dithiocarbamate (MoDTC),molybdenum dithiophosphate (MoDTP), and amine salts of molybdic acid.

Examples of the rust inhibitor include fatty acids, alkenylsuccinic acidhalf esters, fatty acid soaps, alkylsulfonic acid salts, polyhydricalcohol fatty acid esters, fatty acid amines, oxidized paraffins, andalkyl polyoxyethylene ethers.

Examples of the metal deactivator include benzotriazole-based compounds,tolyltriazole-based compounds, thiadiazole-based compounds,imidazole-based compounds, and pyrimidine-based compounds.

Examples of the demulsifier include anionic surfactants, such assulfuric acid ester salts of castor oil and petroleum sulfonic acidsalts; cationic surfactants, such as quaternary ammonium salts andimidazolines; polyoxyalkylene polyglycols and dicarboxylic acid estersthereof; and alkylene oxide adducts of an alkylphenol-formaldehydepolycondensate.

Examples of the anti-foaming agent include silicone oils, fluorosiliconeoils, and fluoroalkyl ethers.

[Various Properties of Lubricating Oil Composition]

A kinematic viscosity at 40° C. of the lubricating oil composition of anembodiment of the present invention is preferably 10 to 100 mm²/s, morepreferably 13 to 75 mm²/s, and still more preferably 25 to 55 mm²/s.

A viscosity index of the lubricating oil composition of an embodiment ofthe present invention is preferably 100 or more, more preferably 120 ormore, and still more preferably 130 or more.

The lubricating oil composition of the present invention not only hasexcellent oxidation stability but also is favorable in an effect forsuppressing the generation of squeal and braking properties, andtherefore, it is suitably applicable to machines equipped with at leastone of a wet type brake and a wet type clutch.

With respect to the lubricating oil composition of an embodiment of thepresent invention, on the occasion of performing the “Test of OxidationStability of Lubricating Oils for Internal Combustion Engine” (ISOT) inconformity with JIS K2514-1 at a test temperature of 150° C. for 168hours, the amount of sludge generated after the test as measured inconformity with JIS B9931 is preferably less than 2.0 mg/100 mL, morepreferably less than 1.5 mg/100 mL, and still more preferably less than1.0 mg/100 mL.

It may be said that as the amount of sludge is lower, the lubricatingoil composition has more excellent oxidation stability even at a hightemperature.

In this specification, the aforementioned amount of sludge means a valueas measured in conformity with the method described in the section ofExamples as mentioned later.

With respect to the lubricating oil composition of an embodiment of thepresent invention, on the occasion of performing a high-pressure pistonpump test with a high-pressure piston pump test apparatus (pump:BOSCH-REXROTH A2F10) in conformity with JCMAS P045 under a condition ofa pump pressure of 35 MPa, a sample oil temperature of 80° C., and anair blowing amount of 1.0 L/h for 500 hours, the amount of sludgegenerated after the test as measured in conformity with JIS B9931 ispreferably less than 3.0 mg/100 mL, more preferably less than 2.0 mg/100mL, and still more preferably less than 1.0 mg/100 mL.

It may be said that as the amount of sludge is lower, the lubricatingoil composition has more excellent oxidation stability even under a highpressure.

In this specification, the aforementioned amount of sludge means a valueas measured in conformity with the method described in the section ofExamples as mentioned later.

With respect to the lubricating oil composition of an embodiment of thepresent invention, on the occasion of measuring a kinematic frictioncoefficient at an oil temperature of 80° C. under a load of 0.5 MPa byusing a low-speed slip test apparatus in conformity with JASO M349, fromthe viewpoint of making the effect for suppressing the generation ofsqueal and the braking properties favorable, a ratio of a kinematicfriction coefficient pi at a rotational speed of 1 rpm to a kinematicfriction coefficient μ₅₀ at a rotational speed of 50 rpm [μ₁/μ₅₀] ispreferably 0.80 or more and less than 1.00, more preferably 0.80 or moreand less than 0.95, and still more preferably 0.81 or more and less than0.90.

The kinematic friction coefficient μ₁ at a rotational speed of 1 rpm ispreferably 0.100 or more and less than 0.150, more preferably 0.105 ormore and less than 0.140, and still more preferably 0.110 or more andless than 0.130.

The kinematic friction coefficient hi can be considered to be akinematic coefficient just before stop, whereas the kinematic frictioncoefficient μ₅₀ can be considered to be a kinematic coefficient duringoperation. The ratio [μ₁/μ₅₀] is a physical properties value serving asan index of the braking properties, and so long as it falls within theaforementioned range, it may be said that the braking properties arefavorable.

In this specification, the aforementioned kinematic friction coefficientpi and ratio [μ₁/μ₅₀] mean values as measured in conformity with themethod described in the section of Examples as mentioned above.

With respect to the lubricating oil composition of an embodiment of thepresent invention, the wear amount of vanes and a cam ring as measuredunder a condition described in the section of Examples as mentionedlater in conformity with ASTM D2882 on the occasion of driving a basepump (a product name: “V-104C”, manufactured by Vickers) for 100 hoursis preferably less than 40 mg, more preferably less than 36 mg, stillmore preferably less than 30 mg, and yet still more preferably less than25 mg.

[Application of Lubricating Oil Composition]

Even if the lubricating oil composition of the present invention isapplied for lubrication of a wet type brake or a wet type clutch, it isable to suppress the generation of squeal and to make the brakingproperties favorable, and therefore, it is preferred that thelubricating oil composition of the present invention is used formachines equipped with a wet type brake or a wet type clutch and used asa hydraulic fluid composition.

The machine is preferably a construction machinery, and more preferablya crane.

Examples of the construction machinery as referred to herein includecranes, such as a mobile crane, a stationary crane, and a derrick;excavators, such as a hydraulic excavator, a compact excavator, and awheel type hydraulic excavator; land grading machines, such as abulldozer; loaders, such as a wheel loader; transporting machines, suchas a rough terrain hauler; compacting machines, such as a vibratoryroller; dismantling machines, such as a breaker; foundation workmachines, such as a pile driver and an earth auger; concrete/asphaltmachines, such as a concrete pump vehicle; an elevating work platform, apaving machine, a shielding machine, a boring machine, and a snowblower.

Namely, since the lubricating oil composition of the present inventionhas excellent braking properties, it is preferably a hydraulic fluidcomposition which is used for construction machineries for which brakingproperties are especially required, and specifically, it is morepreferably a hydraulic fluid composition which is used for cranes.

That is, the present invention may also provide the following machinesand method of using a lubricating oil composition.

(1) A machine equipped with at least one of a wet type brake and a wettype clutch, using a lubricating oil composition containing a base oil(A), zinc dithiophosphate (B), a metal sulfonate (C), and an ashlessfriction modifier (D) containing a boronated alkenyl succinimide (D1).

(2) A method of using a lubricating oil composition, including using alubricating oil composition containing a base oil (A), zincdithiophosphate (B), a metal sulfonate (C), and an ashless frictionmodifier (D) containing a boronated alkenyl succinimide (D1) for amachine equipped with at least one of a wet type brake and a wet typeclutch.

Preferred embodiments of the lubricating oil composition as prescribedin the above (1) and (2) are those as mentioned above.

The aforementioned machine is preferably a construction machinery, andmore preferably a crane.

[Production Method of Lubricating Oil Composition]

The present invention also provides a production method of a lubricatingoil composition, including the following step (I).

Step (I): A step of blending a base oil (A) with zinc dithiophosphate(B), a metal sulfonate (C), and an ashless friction modifier (D)containing a boronated alkenyl succinimide (D1).

The components (A), (B), (C), and (D) which are blended in theaforementioned step (I), and the component (E) and the other additivesfor lubricating oil, which are blended, as the need arises, are those asmentioned above, and the kinds of suitable components and the content ofeach of the components are also those as mentioned above.

In the present step, the other additives for lubricating oil than thesecomponents may also be blended at the same time.

Each of the components which are blended in the step (I) may be blendedafter being converted into a form of a solution (dispersion) uponaddition with a diluent oil or the like. It is preferred that afterblending the respective components, the blend is stirred and uniformlydispersed by a known method.

EXAMPLES

Next, the present invention is described in more detail by reference toExamples, but it should be construed that the present invention is by nomeans limited by these Examples. Various properties of the respectivecomponents used in the Examples and Comparative Examples and theobtained lubricating oil compositions were measured in conformity withthe following methods.

<Kinematic Viscosity at 40° C. and 100° C.>

Measured in conformity with JIS K2283.

<Viscosity Index>

Measured in conformity with JIS K2283.

<Content of Each of Zinc Atom, Calcium Atom, Boron Atom, and PhosphorusAtom>

Measured in conformity with JPI-5S-38-03.

<Content of Nitrogen Atom>

Measured in conformity with JIS K2609.

<Content of Sulfur Atom>

Measured in conformity with JIS K2541-6.

<Base Number (Perchloric Acid Method)>

Measured in conformity with JIS K2501.

<Weight Average Molecular Weight (Mw) and Number Average MolecularWeight (Mn)>

A value obtained by performing the measurement with a gel permeationchromatograph (“1260 Type HPLC”, manufactured by Agilent) under thefollowing condition and expressing in terms of standard polystyrene wasused.

(Measurement Condition)

-   -   Column: Two “Shodex LF404” columns connected in order    -   Column temperature: 35° C.    -   Developing solvent: Chloroform    -   Flow rate: 0.3 mL/min

Examples 1 to 3 and Comparative Examples 1 to 3

The following mineral oil and various additives were added in blendingamounts shown in Table 1 and thoroughly mixed to prepare lubricating oilcompositions, respectively.

Details of the mineral oil and various additives used in the Examplesand Comparative Examples are as follows.

(Component (A))

-   -   “Mineral oil”: Mixed mineral oil of 100N mineral oil grouped in        Group 3 and 500N mineral group in Group 2 by the API category        ((100N mineral oil)/(500N mineral oil)=86/14 (mass ratio)),        kinematic viscosity at 40° C.=23.57 mm²/s, viscosity index=118

(Component (B))

-   -   “ZnDTP”: Zinc dialkyldithiophosphate (a compound represented by        the general formula (b-1), wherein R¹ to R⁴ are each a        2-ethylhexyl group), content of zinc atom=9.9% by mass, content        of phosphorus atom=8.0% by mass, content of sulfur atom=16.6% by        mass

(Component (C))

-   -   “Ca sulfonate”: Overbased calcium sulfonate, base number        (perchloric acid method)=450 mgKOH/g, content of calcium        atom=20.0% by mass, content of sulfur atom=1.4% by mass

(Component (D1))

-   -   “Boronated alkenyl succinimide”: Boronated product of        polybutenyl succinic monoimide having a polybutenyl group and        having a number average molecular weight (Mn) of 1,000 (a        boronated product of a compound represented by the general        formula (d-11)), content of boron atom=3.1% by mass, content of        nitrogen atom=3.8% by mass, mass ratio (B/N) of boron atom to        nitrogen atom=0.82

(Component (D2))

-   -   “Oleylamine”: Primary unsaturated amine represented by the        general formula (b-2), wherein z1=z2=8, content of nitrogen        atom=5.2% by mass

(Component (E1))

-   -   “Phenol-based antioxidant”: 2,6-Di-t-butyl-4-methylphenol (DBPC)

(Component (E2))

-   -   “Amine-based antioxidant”: Alkylated diphenylamine, content of        nitrogen atom=4.6% by mass

(Other Additives)

-   -   “Viscosity index improver”: Polymethacrylate having a weight        average molecular weight (Mw) of 30,000 to 45,000    -   “Other additives”: Mixed additive of a flow point depressant, an        extreme pressure agent, a rust inhibitor, a copper deactivator,        a demulsifier, and an anti-foaming agent

With respect to the lubricating oil compositions prepared in theExamples and Comparative Examples, the following tests were performed.The results thereof are shown in Table 1.

(1) Test of Oxidation Stability of Lubricating Oils for InternalCombustion Engine (ISOT)

The test of oxidation stability of lubricating oils for internalcombustion engine (ISOT) in conformity with JIS K2514-1 was performed ata test temperature of 150° C. for 168 hours. Then, the amount of sludgegenerated after the test (mg/100 mL) was measured in conformity with JISB9931.

(2) High-Pressure Piston Pump Test

The high-pressure piston pump test with a high-pressure piston pump testapparatus (pump: BOSCH-REXROTH A2F10) in conformity with JCMAS P045 wasperformed under a condition of a pump pressure of 35 MPa, a sample oiltemperature of 80° C., and an air blowing amount of 1.0 L/h for 500hours. Then, the amount of sludge generated after the test (mg/100 mL)was measured in conformity with JIS B9931.

(3) Low-Speed Slip Friction Test

A kinematic friction coefficient μ₁ at a rotational speed of 1 rpm and akinematic friction coefficient μ₅₀ at a rotational speed of 50 rpm weremeasured with a low-speed slip test apparatus (a product name:“L.V.F.A”, manufactured by Automax Co., Ltd.) in conformity with JASOM349-12 under a condition of an oil temperature of 80° C. and a load of0.5 MPa. Then, a ratio of the kinematic friction coefficient μ₁ to thekinematic friction coefficient μ₅₀ [μ₁/μ₅₀]was calculated.

(4) Vane Pump Wear Test

Using a vane pump (a product name: “V-104C”, manufactured by Vickers),on the occasion of driving for 100 hours in conformity with ASTM D2882under a condition of a pump pressure of 13.8 MPa, an oil temperature of66° C., a rotational speed of 1,200 rpm, a sample oil amount of 60 L,and a flow rate of 25 L/min, the wear amount (unit: mg) of vanes and acam ring was measured.

TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Composition Component (A): Mineral oilMass % 89.25  89.20  90.89  90.03 89.80  89.85  Component (B): ZnDTPMass % 0.38 0.38 0.75 — 0.38 0.38 Expressed in terms 376    376   720    — 376    376    of Zn (mass ppm) Component (C): Ca sulfonate Mass% 0.45 0.45 0.84 — 0.45 0.45 Expressed in terms 900    900    1800     —900    900    of Ca (mass ppm) Component (D1): Boronate Mass % 0.60 0.600.60 0.60 — — alkenyl succinimide Expressed in terms 186    186   186    186 — — of B (mass ppm) Expressed in terms 228    228    228   228 — — of N (mass ppm) Component (D2): Oleylamine Mass % — 0.05 — 0.050.05 — Expressed in terms — 26    — 26 26    — of N (mass ppm) Component(E1): Phenol-based Mass % 0.60 0.60 — 0.60 0.60 0.60 antioxidantComponent (E2): Amine-based Mass % 0.20 0.20 — 0.20 0.20 0.20antioxidant Viscosity index improver (*1) Mass % 6.30 6.30 6.30 6.306.30 6.30 Other additives Mass % 2.22 2.22 0.62 2.22 2.22 2.22 Sum totalMass % 100.00  100.00  100.00  100.00 100.00  100.00  Content ratio ofcomponent (D1) to component (Mass ratio) — 12.00  — 12.00 — — (D2)[(D1)/(D2)] Properties of hydraulic fluid Kinematic mm²/s 34.26  34.27 34.43  33.75 33.52  33.51  composition viscosity at 40° C. Viscosityindex — 180    180    180    181 182    182    Evaluation (1) ISOTAmount of sludge mg/100 mL 1>   1>   1>   2 1>   1>   items (2) High-Amount of sludge mg/100 mL 1>   1>   1>   3 1>   1>   pressure pistonpump test (3) Low- μ₁ —  0.115  0.111  0.112 0.094  0.089  0.094 speedslip μ₅₀ —  0.140  0.135  0.134 0.127  0.120  0.134 friction test μ₁/μ₅₀— 0.82 0.82 0.84 0.74 0.74 0.70 (4) Vane Wear amount mg 35.6  33.2 24.4  120.1 40.5  42.2  pump wear test (*1): Though blended as asolution diluted with the mineral oil, the blending amount shown inTable 1 expresses a blending amount as expressed in terms of the resincontent exclusive of the mineral oil that is the diluent oil.

From Table 1, the lubricating oil compositions prepared in Examples 1 to3 are low in the amount of sludge in the ISOT and the high-pressurepiston pump test, and therefore, it may be said that the lubricating oilcompositions prepared in Examples 1 to 3 are high in the oxidationstability at a high temperature and a high pressure. In addition, in thelubricating oil compositions prepared in Examples 1 to 3, in view of thefact that the μ₁/μ₅₀ value is 0.80 or more and less than 1.00, it may besaid that the effect for suppressing the generation of squeal is high,and the braking properties are favorable. Furthermore, the lubricatingoil compositions prepared in Examples 1 to 3 are also excellent in thewear resistance.

On the other hand, in the lubricating oil compositions prepared inComparative Examples 1 to 3, since the μ₁/μ₅₀ value is low, it may besaid that the squeal is liable to be generated, and the brakingproperties are problematic; and in addition, there were brought suchresults that the wear resistance is inferior as compared with Examples 1to 3.

1: A lubricating oil composition, which is to be used for a machineequipped with at least one of a wet type brake and a wet type clutch,comprising a base oil (A), zinc dithiophosphate (B), a metal sulfonate(C), and an ashless friction modifier (D) containing a boronated alkenylsuccinimide (D1). 2: The lubricating oil composition according to claim1, wherein the content of the component (B) as expressed in terms of azinc atom based on the total amount of the lubricating oil compositionis from 100 to 2,000 ppm by mass. 3: The lubricating oil compositionaccording to claim 1, wherein the content of the component (B) asexpressed in terms of a zinc atom based on the total amount of thelubricating oil composition is from 500 to 1,500 ppm by mass. 4: Thelubricating oil composition according to claim 1, wherein the component(C) contains calcium sulfonate. 5: The lubricating oil compositionaccording to claim 1, wherein the content of the component (C) asexpressed in terms of a metal atom based on the total amount of thelubricating oil composition is from 200 to 4,000 ppm by mass. 6: Thelubricating oil composition according to claim 1, wherein the content ofthe component (C) as expressed in terms of a metal atom based on thetotal amount of the lubricating oil composition is from 1,000 to 3,500ppm by mass. 7: The lubricating oil composition according to claim 1,wherein the content of a metal salicylate based on the total amount ofthe lubricating oil composition is less than 0.03% by mass. 8: Thelubricating oil composition according to claim 1, wherein the component(D1) is a boronated product of a compound represented by the followinggeneral formula (d-11) or (d-12):

wherein, R^(A), R^(A1), and R^(A2) are each independently an alkenylgroup having a weight average molecular weight (Mw) of 500 to 3,000;R^(B), R^(B1), and R^(B2) are each independently an alkylene grouphaving 2 to 5 carbon atoms; and x1 is an integer of 1 to 10, and x2 isan integer of 0 to
 10. 9: The lubricating oil composition according toclaim 1, wherein a mass ratio [B/N] of a boron atom to a nitrogen atomconstituting the component (D1) is from 0.2 to 3.0. 10: The lubricatingoil composition according to claim 1, wherein the content of thecomponent (D1) as expressed in terms of a boron atom based on the totalamount of the lubricating oil composition is from 30 to 600 ppm by mass.11: The lubricating oil composition according to claim 1, wherein thecomponent (D) contains the component (D1) and an alkenylgroup-containing unsaturated amine (D2). 12: The lubricating oilcomposition according to claim 11, wherein a content ratio of thecomponent (D1) to the component (D2) [(D1)/(D2)] is from 2 to 100 interms of a mass ratio. 13: The lubricating oil composition according toclaim 1, wherein on the occasion of measuring a kinematic frictioncoefficient at an oil temperature of 80° C. under a load of 0.5 MPa byusing a low-speed slip test apparatus in conformity with JASO M349, aratio of a kinematic friction coefficient μ₁ at a rotational speed of 1rpm to a kinematic friction coefficient μ₅₀ at a rotational speed of 50rpm [μ₁/μ₅₀] is 0.80 or more and less than 1.00. 14: A machine equippedwith at least one of a wet type brake and a wet type clutch, comprisingthe lubricating oil composition according to claim
 1. 15: A method ofusing a lubricating oil composition, comprising using the lubricatingoil composition according to claim 1 for a machine equipped with atleast one of a wet type brake and a wet type clutch.